In a message dated 98-07-09 17:11:25 EDT, st_lupus@email.msn.com writes:
> Okay, I think I've calmed down enough to ask for help on this problem
> without using any swear words. Basically the problem is this: Last
Friday,
> I replaced my points ignition on my 74 TR6 with a Crane electronic
ignition.
> It seemed to run beautifully, no hesitation and didn't miss once. However
> that night, while driving home I noticed that all the lights seemed pretty
> dim and that the volt meter was rapidly dropping. The solution was
obvious,
> drive w/o the lights and pray I made it home. With the aid of a little
luck
> and a sympathetic policeman, I was able to coast the last few feet into my
> parking spot.
>
> Basically when running the car I am not getting any charge into the battery
> at all. The voltage across the battery drops when the car is running.
I've
> spent the last week trying to figure out what the problem is and can't
> figure the damn (oops there I go) thing out. The obvious culprit was the
> alternator (lucas 2 wire regulator), but having it rebuilt (twice) didn't
> help at all. The Ign light comes on when the key is in the on position, but
> goes off as soon as the car is started.
OK, this is going to call for a little detective work! Assuming your
alternator is good, (and you have tested it to confirm that, per your latest
post), then the problem most likely is in the wiring somewhere, or you have a
very bad battery (both items mentioned by Dave Massey and Malcolm Walker - and
good advice, btw).
The first thing you need to do is check out the VTR article on how an
alternator works, which will help you as you trouble shoot the problem. The
URL is:
http://www.vtr.org/maintain/alternator-overview.html
If it is the battery, then it will drag the alternator voltage down with it.
Since the warning light sees battery voltage on one side, and alternator
voltage on the other, it will not light under these conditions. I doubt that
this is the problem, though, as that would put an extreme load on the
alternator, and you would probably get smoke! Not an impossibility, but
unlikey. That battery can be checked at the same place where you had the
alternator checked. And, if it were the battery, you would notice it when you
tried to start the car, as the cranking would be slow at best.
If it is not the battery, then it must be the wiring. An alternator needs
three connections to work: The warning light connection, the system voltage
monitoring connection, and the output connection.
Since the red light comes on when you turn on the key, and goes out when the
engine is running, it is safe to say that this connection is OK (and a good
indication that the alternator is working).
You said you have an alternator with a "Lucas 2 wire regulator." This may be
where your problem lies. TR6s came with a three wire input plug in '74. If you
are missing one of the connections, that would account for the low voltage in
the car.
Take a look at the back of the alternator. You should have three wires - one
small brown/yellow, one small Brown, and one large Brown. The small
Brown/yellow is the warning lamp wire, the small Brown is the voltage
monitoring input, and the large brown wire is the output.
Check for voltage on the small brown wire. There should be 12 volts on this
wire at all times, key on or off (test it with the key off). If you don't have
12 volts, trace the wires to find out where the break is. Most likely, it will
be at the main battery cable connector, as pointed out by Dave.
If you do have 12 volts, look for a break in the large Brown wire, probably at
the same connector as above.
You should, as a matter of course, check, and clean if needed, the battery
cable to the starter solenoid. I don't think this is your problem, if you are
having no trouble cranking over the engine.
It is possible that you have a two wire alternator, but if so, it came from
another car, not a TR6. Some MGs, for example used a two wire. In this case,
the small Brwon wire is internal to the alternator, and measures system
voltage at the connection to the output terminal, the large brown wire. If
that is the case, then just check for bad connections in the large Brown wire.
That is just about all I can think of. Let me know if that helped. If not,
I'll try to think of something else.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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